As a result of the June 2012 Supreme Court decision that made Medicaid expansion optional for states, many childless low-income adults in non-expansion states are left without access to affordable coverage. Not only does this expansion decision affect individuals, but it has important, unknown impacts on providers serving these individuals, including health centers. In the 29 states and districts that have expanded, most previously uninsured patients served by health centers will gain coverage. In the 22 states that have not expanded as of January 2015, most individuals under 100% of the federal poverty level (FPL) who would have otherwise gained coverage are left uninsured; for health centers in these states, this will likely result in lesser patient revenue. Given that sufficient revenue is required to maintain staffing levels, meet demand, and provide high quality care, this may also affect capacity to provide care and the quality of care delivered. It may also compromise health centers' continued ability to combat racial/ethnic disparities in quality. This is important becaus health centers play a critical role in providing access to quality primary care for vulnerable populations who would otherwise be without access to such care. Given the projected increase in demand for primary care services coupled with health center funding reductions from states and local entities, understanding how the decision to expand versus not expand Medicaid affects the quality performance of health centers and their capacity to provide care is essential to protecting health centers and the vulnerable populations they serve. Our specific aims are: (1) to assess the early impact of Medicaid expansion on the quality performance of health center grantees, which will include a pre (2007-2013) and post (2014-2015) assessment of 11 process and 3 outcome measures; a sub-aim will be to assess to what extent, if any, Medicaid expansion affects racial/ethnic disparities in quality, and (2) to assess the early impact of Medicaid expansion on health center grantees' capacity to provide care, which will include a pre (2007-2013) and post (2014-2015) assessment of change in total number of services provided and total number of patients served, by category of service. Our hypothesis is that compared to health centers in non-expansion states, centers in Medicaid expansion states will experience higher quality performance in the two years following expansion, as well as reduced racial/ethnic disparities in quality. We also hypothesize that capacity to provide care will be higher in centers in expansion states compared to non-expansion states. We will use HRSA's 2007-2015 Uniform Data System (UDS) data, which are reported annually at the health center level. Propensity score matching of cases (expansion) versus controls (non-expansion) will be done at the health center level and an econometric difference-in-differences framework will be used to estimate the effect. Findings will contribute to the evidence base available to states looking to potentially expand their Medicaid programs, while helping states better understand how some of their most vulnerable populations are affected by Medicaid expansion.